Forming array contacts in semiconductor memories

ABSTRACT

Array contacts for semiconductor memories may be formed using a first set of parallel stripe masks and subsequently a second set of parallel stripe masks transverse to the first set. For example, one set of masks may be utilized to etch a dielectric layer, to form parallel spaced trenches. Then the trenches may be filled with a sacrificial material. That sacrificial material may then be masked transversely to its length and etched, for example. The resulting openings may be filled with a metal to form array contacts.

BACKGROUND

This relates generally to semiconductor memories, such as non-volatile memories or volatile memories. Particularly, it relates to forming array contacts in memories.

Semiconductor memories may be volatile or non-volatile memories. Examples of volatile memories include dynamic random access memories (DRAMs) and static random access memories (SRAMs). Examples of non-volatile memories include Flash memories and resistive random access memories (ReRAM), such as phase change memories, to mention a few examples.

Typically, semiconductor memories include an array made up of parallel conductive rows and parallel conductive columns perpendicular to the rows. Selectable memory cells are formed at the intersections of those rows and columns.

Array contacts electrically connect elements in the array to metallization lines overlying the array. The array contacts then are conductive vias. With increasingly smaller memory cell sizes, array contacts need to effectively scale correspondingly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged, top plan view of one embodiment of the present invention at an early stage of manufacture;

FIG. 2 is a reduced cross-sectional view taken generally along the line 2-2 in FIG. 1;

FIG. 3 is a cross-sectional view corresponding to FIG. 2 at a subsequent stage in accordance with one embodiment;

FIG. 4 is a top plan view at a subsequent stage in accordance with the embodiment of FIGS. 1-3;

FIG. 5 is an enlarged, cross-sectional view taken generally along the line 5-5 in FIG. 4;

FIG. 6 is an enlarged, cross-sectional view of an alternate embodiment at a stage subsequent to the stage shown in FIG. 3 in accordance with one embodiment;

FIG. 7 is an enlarged, cross-sectional view at a subsequent stage to that shown in FIG. 6 in accordance with one embodiment;

FIG. 8 is an enlarged top plan view of still another embodiment;

FIG. 9 is an enlarged top plan view at a subsequent stage; and

FIG. 10 is an enlarged top plan view at a subsequent stage.

DETAILED DESCRIPTION

In accordance with some embodiments, array contacts can be formed without some of the limitations typically imposed by conventional lithographic techniques. For example, conventional array contacts for high density arrays may be made using a dipole illumination mode for lithographic contact hole definition. One problem with this technique is that the illumination mode results in an elliptical shape for the contact where the X/Y ratio is reduced with reducing critical pitch. Overly elliptical contacts can sometimes result in integration issues in terms of contact to gate distance.

In accordance with some embodiments of the present invention, at least two perpendicular masks and definition stages are used to define the array contacts instead of using the single mask, dipole illumination mode technique. This may result, in some embodiments, in reducing the integration issues that sometimes arise from an overly elliptical contact shape.

Referring to FIG. 1, a memory array 10 may include a plurality of parallel, spaced conductive lines 16, extending generally perpendicularly to parallel, spaced active areas 12, situated below the lines 16. The active areas are the regions where the memory cells are formed. The regions surrounding the lines 16 may be filled with a dielectric 14, such as pre-metal deposition (PMD) oxide, over an etch stop layer (not shown) such as borderless nitride for example. However, other dielectrics may be used as well. The conductive lines 16 may, for example, be control gates, in a Flash memory embodiment. However, the present invention is applicable to any semiconductor memory technology, including volatile and non-volatile memories.

A plurality of spaced parallel masks 18 may be aligned over the conductive lines 16, each mask 18 having dimensions slightly larger than the conductive lines 16. Thus, the masks 18 may extend in the same direction as the conductive lines 16 and generally perpendicularly to the active areas 12 in one embodiment. The masks 18 may be patterned photoresist for example.

Referring to FIG. 2, the conductive lines 16 extend perpendicularly across the active areas 12. Other elements are not shown for simplicity. In this case, spaced, parallel tapered trenches 20 are formed between adjacent conductive lines 16. The trenches 20 extend in the same lengthwise direction and have the same pitch as the conductive lines 16 in this embodiment. The trenches 20 may be formed using the masks 18, shown in FIG. 1 with dry etching for example. The mask 18 widths may be altered by the etching process. The etching may stop on an etch stop layer (not shown) at the bottom of the dielectric 14. In some embodiments, the etching is highly selective of the etch stop.

After etching, the masks 18 may be removed. In some embodiments, the trenches 20 may taper inwardly from top to bottom as a result of the selected etching techniques. However, in other embodiments, vertical wall trenches may be formed.

Referring to FIG. 3, at this second masking stage, the trenches 20 may be filled with a trench filler 24 and planarized to the height of the dielectric 14. Examples of trench filler materials include nitrides, such as SiON, polysilicon, etc. Parallel spaced masks 22, formed of any suitable material, including photoresist, may extend generally perpendicularly to the lengths of the filled trenches 24. The masks 22 may cover the region between the active areas 12, shown in FIG. 1. The width of the masks 22 determines the desired spacing between resulting, later formed array contacts, as well as the thicknesses of those array contacts. A dry etching process used with masks 22 may be very selective to the selected trench filler 24, in some embodiments.

Moving to FIG. 4, the filled trenches 24 extend generally parallel to the conductive lines 16 and may be situated between adjacent conductive lines. In the direction perpendicular to the trenches 24, the active areas 12 extend parallel to one another. An array contact 26 may be formed in the active areas at the intersection between a trench filler 24 and an active area 12. Other array contact pitches may also be used.

Thus, as shown in FIG. 5, the array contacts 26 are formed at the locations never covered by the masks 18 or 22 (which have been removed at this point). The masks 18 and 22 are arranged perpendicularly to one another. An etchant may be used with the mask 22, which etchant is highly selective of the pre-metal deposition oxide 14. As a result, only the trench filler 24 is removed. The masks 22 may then removed as well.

The resulting etched holes in the trench filler 24 may then filled by standard barrier layers and metal, such as tungsten. Then, a standard chemical mechanical planarization process may be utilized to form the array contacts 26, shown in FIG. 5. The array contacts 26 may be columnar with a square or rectangular cross-section. The array contacts may taper toward the semiconductor substrate. Thus, the contacts 26 may be high aspect ratio or elongate, truncated pyramids. In some cases, the resulting array contacts 26 are more circular or elliptical because the corners tend to etch away.

Referring to FIG. 6, in accordance with a dual damascene embodiment, in the same region used to form the array contacts 26, the filled trenches 24 are partially etched out, as indicated at 28. A dual damascene structure can be formed in the same vertical space that was used to form the array contacts 26 in FIG. 5 in some embodiments. This may be important, in some embodiments, because the amount of vertical space may be limited. However, in some embodiments, the etch out step may not be used. The etch out step entirely removes the upper portion of the trench filler 24, extending into the page in FIG. 6, and leaving a vertically shortened trench filler. A suitable wet etchant that selectively etches the trench filler 24 may be used in some embodiments.

Then, as shown in FIG. 7, the remaining trench filler 24 may be removed at the intersections of masks as described previously, resulting in the array contacts 32. Where the upper layer of the trench filler 24 was removed, spaced parallel metal lines 30 may extend transversely to the conductive lines 16 and have array contacts 32 extend downwardly from the metal lines 30 between adjacent conductive lines 16. These metal lines may, for example, be used as row or bit lines. The metal lines 30 may be formed of the same or different materials.

Of course, the same process may be done in the reverse order wherein the structure is first masked off perpendicularly to the direction of the conductive lines 16 by forming masks 40 overlying the regions between adjacent active areas 12, as shown in FIG. 8. Dry etching may be used to form trenches 42 in the dielectric 14 between masks 40.

The intervening trenches 42 may be trench filled, for example, by a suitable material 44, as shown in FIG. 9. Then the trench fill material 44 may be etched back to the height desired.

Thereafter the array contacts 46 may be formed by etching out the filler material using masks 48 shown in FIG. 10. The contacts 46 are found at the intersections of two masks, as shown in FIG. 10, by metal filling, followed by chemical mechanical planarization.

References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present invention. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application.

While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention. 

What is claimed is:
 1. A method comprising: forming a semiconductor memory array; forming a dielectric layer over said array; forming parallel, spaced trenches through said layer; filling said trenches with a filler material; forming a plurality of masks extending generally perpendicularly to the length of said filled trenches; etching out the exposed portions of said filled trenches to form etched out portions; and filling said etched out portions with a metal.
 2. The method of claim 1 including etching out an upper portion of said filled trenches and leaving a lower portion of said filled trenches.
 3. The method of claim 2 including forming array contacts coupled to a metal line.
 4. The method of claim 3 including forming said metal line and said array contacts in the same metallization.
 5. The method of claim 1 including forming array contacts and metal lines in a dual damascene process.
 6. The method of claim 1 including forming parallel spaced active areas and forming said trenches parallel to the length of the active areas.
 7. The method of claim 1 including forming parallel spaced active areas and forming said trenches perpendicular to the length of the active areas.
 8. A method comprising: forming a semiconductor memory array; covering said array with a dielectric material; forming a plurality of parallel spaced filled trenches in said dielectric material; forming a plurality of spaced openings along the length of each of said trenches; and filling said openings with a metal to form array contacts.
 9. The method of claim 8 including forming said openings using a plurality of spaced parallel masks extending generally transversely to masks used to form said trenches.
 10. The method of claim 8 including etching out an upper portion of said filled trenches and leaving a lower portion of said filled trenches.
 11. The method of claim 10 including forming metal lines in said etched out upper portion of said trenches.
 12. The method of claim 11 including forming array 2 contacts extending transversely to said metal lines using said openings.
 13. The method of claim 8 including forming array contacts of metal lines in a dual damascene process.
 14. The method of claim 8 including forming spaced active areas and forming said trenches parallel to the length of said active areas.
 15. The method of claim 8 including forming parallel spaced active areas and forming said trenches perpendicular to the lengths of the active areas. 